The vasodilator kallikrein-kinin system was studied in white and black hypertensive and normotensive subjects. Excretion of urinary kallikrein was significantly lower in black than in white subjects (5.4 vs 10 TU/day, p less than .01) but did not correlate with excretion of kinins and neither correlated with blood pressure. Black hypertensives had values of plasma bradykinin twice those of normal subjects or white hypertensives (p less than .001). Urinary kallikrein doubled during restriction of dietary salt but urinary kinins and plasma bradykinin remained unchanged. The findings are consistent with racial differences in the kallikrein-kinin system but do not support decreased vasodilator activity of the system as a factor predisposing to hypertension. BIBLIOGRAPHIC REFERENCES: Gillin, J.C., Horwitz, D., and Wyatt, R.J.: Pharmacologic Studies of Narcolepsy Involving Serotonin, Acetylcholine, and Monoamine Oxidase. In Guilleminault, C., Dement, W.C., and Passouant, P. (Ed) Narcolepsy. Advances in Sleep Research, Vol 3, 1976. Spectrum Publications, Inc., New York. Horwitz, D., Thorgerirsson, S.S., and Mitchell, J.R.: The Influence of Allopurinol and Size of Dose on the Metabolism of Phenylbutazone in Patients with Gout. Eur. J. Clin. Pharmacology. In press, 1977.